booting using grub2 and the following menu entry which works fine on the distribution iso and on a similarly generated iso from 4.4.0-beta003 but not on 4.4.1-beta002 even with no changes in the extract.menuentry "SystemRescueCd (isoloop) test.iso docache" { loopback loop /test.iso linux (loop)/isolinux/rescue64 docache nomodeset vga=791 setkmap=us dostartx isoloop=test.iso initrd (loop)/isolinux/initram.igz}

You can ignore this one. Operator error. Since I only changed initram.igz I skipped the recreate squashfs stage which is of course fatal after an extract since there is no longer a sysrcd.dat file which makes booting impossible.